1. Field of the Invention
The present invention is related to the field of signal transmission.
2. Related Art
Signal transmission between electronics appliances can be carried out in various formats via digital and analog interfaces. A signal has traditionally been transmitted in an analog format using an analog interface. As a result of recent developments in digital signal processing technologies, a digital interface is nowadays becoming a major trend in signal transmission. Particularly, the development of standards regarding digital interfaces, such as IEEE1394, allows digital signals in various formats to be transmitted through a single digital interface.
As technology transitions from analog to digital signal processing, signals may be generated in various formats. The various formats that may be transmitted, including analog, are not always transmitted in one particular format. That is, analog signals co-exist along with digital signals. Because of this, some appliances are designed to cope with signals in different formats, digital and analog. In fact, some transmitters can provide a signal in a digital format to a digital interface while transmitting an analog signal via an analog interface. Receivers have both a digital input terminal and an analog input terminal, so that they are capable of receiving both digital and analog signals.
Under such a circumstance, it is vital to ensure that a signal is being received at an appropriate input terminal of a receiver, either digital or analog, otherwise the receiver cannot operate correctly.
FIG. 1 illustrates an exemplary arrangement of a signal transmitting system comprising a digital video high speed (DVHS) tape recorder/player 10 and a digital TV (DTV) 12. The DVHS 10 and the DTV 12 are connected with each other via a digital interface cable 14 as well as an analog video/audio cable 16. In this arrangement, the DVHS 10 and the DTV 12 work as a transmitter and a receiver, respectively.
The DVHS 10 is a digital video/audio recorder developed based on the conventional analog VHS. The DVHS 10 is capable of recording and playing analog signals in the VHS format. It also operates with a digital signal, i.e., capable of digital recording. The DVHS 10 does not encode or decode a signal. Thus, the DHVS 10 records and plays a digital signal in the unchanged original format. Accordingly, the DTV 12 has a decoder to decode the digital signal from the DVHS 10 into an analog signal so that images and voices are monitored on the DTV 12.
Since no regulation is applied to the recording format, it is probable that a digital signal and an analog signal are recorded on a single recording medium, e.g., videotape. FIG. 2 shows an exemplary signal pattern recorded on videotape 20, on which an analog signal is recorded after a digital signal.
Within the arrangement described above, for instance, the format of the signal transmitted from the DVHS 10 will change from a digital format to the analog format at some point as the videotape 20 is running. If a change of format has occurred, the analog signal is provided to the wrong input terminal, and, consequently, the DTV 12 will not be able to reproduce a picture and/or voice based upon the incoming signal because of the difference of the format. In other words, a picture and voice on the DTV 12 will be suddenly lost as soon as the signal format changes.
In order to avoid such a faulty state, it is necessary to switch between the digital and analog input terminals of the receiver. Therefore, the incoming signal is obtained from an appropriate input terminal no matter what the format of the incoming signal format is, digital or analog.
For the foregoing reasons, there is a need for switching between input terminals based on transmitted signal format.
The present invention is directed to a method and apparatus that satisfies the need for switching between input terminals based on a transmitted signal format.
A transmitted signal is received at a first input terminal of a receiver. Once the signal is received, a command is issued when a format of the transmitted signal changes. As a result of the issued command, automatic switching to a second input terminal of the receiver from the first input terminal to receive the transmitted signal.
More specifically, the method includes selecting an input terminal of the receiver, either a digital input terminal or an analog input terminal, when the command is issued.
In this method, a first command may be issued when the transmitted signal format changes from a digital format to an analog format. The receiver will then select its analog input terminal to receive the incoming signal when the command is received. Also, a second command may be issued when the transmitted signal format has changed from an analog format to a digital format, so that the receiver will select the digital input terminal according to the second command.
An apparatus to which the present invention is directed includes a transmitter that has a command generator. The command generator issues a command to the receiver when a format of the signal changes from digital to analog. The command generator may also issue another command when the format changes from analog to digital. Such commands may be transmitted through a digital interface that connects the transmitter and receiver with each other, or through an additional communication line.
The apparatus also includes a receiver including a first input terminal, a second input terminal, a digital signal interface coupled to the first terminal, a digital signal processor coupled to the digital signal interface, and a selector for selecting the first or second input terminal to receive an incoming signal based upon a format of the incoming signal. More specifically, the selector selects an input terminal based on the command issued from the transmitter. Each input terminal may have been associated with a signal format to be received at the input terminal.
According to the present invention, since the receiver can select an appropriate input terminal itself, the receiver can operate properly, even if the format of an incoming signal changes from a first format to a second format. Therefore, there is no requirement for a user to perform a rerouting operation.